I dunno, I always treat "insanity" through Mythos Exposure as a fictional condition that has nothing to do with actual mental illness. Its symptoms being as described in Lovecraft's stories. I skip the actual diagnostic labels suggested in the rulebook. I personally don't feel the need to make it more "realistic" even in modern settings.
I am no stranger to mental issues myself, but I don't feel offended or alienated by Call of Cthulhu's in-game use of insanity in the slightest.

How's about adding a kind of mini setting to the campaign, adding all the necessary rules, and turning the whole thing into its own game, like what they did with Dark Streets.
Also, for additional French & Indian War material you might want to check out The French & Indian War for Rogue Games' Colonial Gothic RPG. Mystical Throne Entertainment did a supplemental setting book for Colonial Gothic that is set in Portsmouth just before the French & Indian War.
Links:
Colonial Gothic: The French & Indian War
Portsmouth 1745 (Colonial Gothic) [PDF] – Mystical Throne Entertainment
You can get both books in print on demand from DTRPG.

I own the two core books (and the Legend rulebook), but I'm personally not overly impressed. Though I'm certain one could have great fun using the setting there's little there that strikes me as particularly original or inspired. It's all a bit dull. Other sourcebooks may improve on this, I don't know. (I'm also not sold on the Legend system.)
btw, wasn't there a Legend section on the forums?

Kevin Ross' Old West Cthulhu setting Down Darker Trails is indeed in Chaosium's pipeline and a definite must-buy for me, but it's going to be strictly 19th century.
The long overdue d100 game Raiders of R'lyeh, which is going to be set in the 1910s, will include some material on the Mexican Revolution AFAIK. This is still being worked on and preview material given out to KS backers so far looks very promising but there's no telling when it will finally be finished.
Help us Abe, Cakebread & Walton, you're our only hope!

French and Indian War mini setting
Early Old West, California Gold Rush mini setting
But as I already mentioned in another thread a full campaign setting for the Mexican Revolution with culturally appropriate, subtle folk magic would be my dream product. (Link to the discussion.) doomedpc certainly seemed to like the idea!